The present invention relates to a magnetic alloy with ultrafine crystal grains excellent in magnetic properties and their stability, a major part of the alloy structure being occupied by ultrafine crystal grains, suitable for magnetic cores for transformers, choke coils, etc.
Conventionally used as core materials for magnetic cores such as choke coils are ferrites, silicon steels, amorphous alloys, etc. showing relatively good frequency characteristics with small eddy current losses.
However, ferrites show low saturation magnetic flux densities and their permeabilities are relatively low if the frequency characteristics of their permeabilities are flat up to a high-frequency region. On the other hand, for those showing high permeabilities in a low frequency region, their permeabilities start to decrease at a relatively low frequency. With respect to Fe--Si--B amorphous alloys and silicon steels, they are poor in corrosion resistance and high-frequency magnetic properties.
In the case of Co-base amorphous alloys, their magnetic properties vary widely with time, suffering from low reliability.
In view of these problems, various attempts have been made. For instance, Japanese Patent Laid-Open No. 64-73041 discloses a Co--Fe--B alloy having a high saturation magnetic flux density and a high permeability. However, it has been found that this alloy is poor in heat resistance and stability of magnetic properties with time.